The present invention relates to a vehicular height adjusting device disposed between the body of a vehicle and an axle to damp vibrations from the surface of a road in a normal running condition and capable of controlling the height of the vehicle constant at all times irrespective of a sprung weight.
As for this type of a vehicular height adjusting device, there has been developed, for example, such a device as shown in FIG. 3. In this vehicular height adjusting device, when the vehicle equipped with the device is at its standard height, a control orifice 1C is formed in a position not to be covered with a pump cylinder 11. Upon increase of the sprung weight due to loading of goods for example, a shock absorber S contracts as the vehicular height decreases, and the control orifice 1C and a cutout passage 1B get into the pump cylinder 11. While the vehicle is running, the shock absorber S is vibrated due to unevenness of the surface of a road. In an extension stroke of the shock absorber S in the lowered state of the vehicle height, a hydraulic oil in a rod-side chamber C moves into an antirod-side chamber B through a piston 6 equipped with a damping valve. Then, the hydraulic oil in an amount corresponding to a retracting volume of a pump rod 1 from a pump cylinder 11 leaves a reservoir F, passes through a suction pipe 8, a passage 5A formed in the upper portion of an outer shell 5, then passes through a hollow bore 1A formed inside the pump rod 1, opens an induction valve 9 and is introduced into a pump chamber A of a negative pressure.
In a retracting stroke of the shock absorber S, the hydraulic oil in the pump chamber A is discharged from a discharge valve 13, passes through a passage 11A formed between a piston rod 12 and the pump cylinder 11 and flows into the antirod-side chamber B. With an increase in the amount of oil in the antirod-side chamber B caused by repetition of such a self-pumping action, the oil in the antirod-side chamber B flows through a communication hole 2A formed in a disc plate 2 which seals the upper end of the cylinder 3, then through a passage 3A formed between the cylinder 3 and a cap 4, and enters an oil chamber E. Through a boot 7 serving as a contractible partition wall, the oil chamber E is partitioned from a high-pressure gas chamber D with an inert high-pressure gas sealed therein and serves as an oil chamber of an accumulator formed in the shock absorber S.
As a result of the boot 7 being expanded by the internal pressure of the oil chamber E, the volume of the high-pressure gas chamber D is diminished and the internal pressure thereof increases. Consequently, the pressure of the oil chamber E which balances with the pressure of the high-pressure gas chamber D through the boot 7, as well as the pressure of the antirod-side chamber B in communication with the oil chamber E, also increases, resulting in that the repulsive force of the piston rod 12 increases and the shock absorber S extends in proportion to the increase of the said repulsive force, thus causing the vehicular height to increase. With extension of the shock absorber S, the cutout passage 1B formed by cutting out a part of the outer surface of the pump rod 1 goes out of the pump cylinder 11, so that the pump chamber A and the antirod-side chamber B come into communication with each other through the cutout passage 1B and the foregoing self-pumping action vanishes. Thus, the vehicular height does not increase any further.
Next, as the sprung weight decreases due to unloading for example, the shock absorber S extends under the repulsive force of the piston rod 12 and at a speed buffered by the piston 6 equipped with a damping valve, the piston 6 being mounted to the upper end of the piston rod 12. As a result, the control orifice 1C goes out of the pump cylinder 11. During the period from this condition up to the time when the control orifice 1C enters and is closed with the pump cylinder 11, the hydraulic oil in the antirod-side chamber B passes through the control orifice 1C, then through the hollow bore 1A formed inside the pump rod 1 and further through the suction pipe 8, and is returned to a reservoir F, so that the internal pressure of the antirod-side chamber B decreases and the repulsive force of the piston rod 12 also decreases. Consequently, the vehicular height lowers to its standard height.
Numeral 10 denotes a rod guide. The cylinder 3 is fitted on a stepped upper-end portion of a small diameter of the rod guide 10, while the boot 7 is fitted on a stepped large-diameter portion of the rod guide 10. Seals 15 and 16 are mounted inside the rod guide 10 at two stages. The piston rod 12 is guided slidably by means of a bushing 17 which is press-fitted in the lower end portion of the rod guide 10. Numeral 14 denotes a clamping nut for fixing the rod guide 10 to the outer shell 5. Numeral 18 denotes a dust boot for protecting the piston rod from dust.
In the above conventional vehicular height adjusting device, the high-pressure gas chamber D of the accumulator is formed inside the cylinder 5 whose outer diameter is constant and hence its volume is restricted, there has been a problem such that it is difficult to diminish a shock caused by a sudden change in pressure of the oil chamber E at the time of vehicular height adjustment and thereby gently adjust the vehicular height. There also has been a problem such that a beat noise generated at the time of opening and closing of the induction valve and the discharge valve in the vehicular height adjusting motion which is repeated frequently.